Image display devices such as cathode ray tube display devices (CRTs), liquid crystal displays (LCDs), plasma displays (PDPs), electroluminescence displays (ELDs), touch panels, electronic paper displays, and tablet computers are generally provided with an optical layered body for antireflection on the outermost surface. Such optical layered bodies for antireflection suppress reflection of images and reduce the reflectance by scattering or interference of light.
Known as one of optical layered bodies for antireflection is an anti-glare film in which an anti-glare layer with surface roughness is formed on a transparent substrate. The surface roughness on the anti-glare film scatters natural light and thus prevents a decrease in visibility due to reflection of natural light and of images.
Examples of such anti-glare films include a film having an anti-glare layer with surface roughness formed by aggregation of particles like cohesive silica; a film having surface roughness on a surface of an anti-glare layer formed by adding an organic filler to a resin, the particle size of the filler being equal to or greater, and/or equal to or smaller than the film thickness of a coating; a film with surface roughness on a surface of an anti-glare layer formed by phase separation of a resin; and a film produced by lamination of a film with surface roughness to transfer projections and depressions (e.g., Patent Literatures 1, 2).
Such anti-glare films require a certain hardness in addition to the mentioned anti-glare property, and preferably have a hardness equal to or higher than “H” of the pencil hardness test specified in JIS K5600-5-4 (1999), for example. Such anti-glare films with a high hardness are known to be produced by forming an anti-glare layer containing silica particles (Patent Literature 3).
On the other hand, liquid crystal displays with high definition are recently developed, which require higher performance of anti-glare films. Particularly required are a film achieving, in addition to excellent anti-glare property and optical characteristics, crack prevention during production like post-processing, and having a thin anti-glare layer achieving light weight and cost reduction. A thinner anti-glare layer, however, reduces the hardness of the anti-glare layer which serves as a hard coat layer. Accordingly, required is a film having both hardness and crack prevention.
In a conventional method of adding particles like silica to an anti-glare layer, a transparent substrate and an anti-glare layer need to be thick for sufficiently enhancing the hardness (pencil hardness and scratch resistance) of the hard coat of the anti-glare layer, whereby failing to achieve sufficient crack prevention. Enhancing the hardness of the hard coat of the anti-glare layer without increasing the film thickness of the substrate and of the anti-glare layer requires adding an excessive amount of silica particles. This, however, causes loss of adhesion to the substrate, insufficient crack prevention due to compatibility of hardness and fragileness, and poor blackness visibility due to reduced light transmittance of the anti-glare film, in other words, deterioration of image contrast. In addition, the anti-glare layer fails to obtain the desired rough surface and good anti-glare property.